Heat shock proteins (Hsp) have emerged as significant factors in the development of a number of cancers. One of the long-term aims of our laboratory is to assess the role of these Hsp in breast cancer malignancy and to progress towards targeting them in therapy. This application, is aimed at study of heat shock transcription factor 1 (HSF1), the protein which activates hsp gene transcription. We aim to study the mechanisms underlying the overexpression and activation of HSF1 in breast cancer. Our hypothesis is that HSF1 is the downstream target of a signaling pathway that is initiated by interaction of the oncogenic factor heregulin with the proto-oncogene HER2/c-erb-b2 on the surface on breast cancer cells. This leads to deactivation of the protein kinase GSK3 and to dephosphorylation of HSF1 on an inhibitory serine residue (Ser303). We aim to show that S303 dephosphorylation blocks inhibitory interactions of HSF1 with the phosphoprotein binding proteins 14-3-3 and SCFFbw7 and thus leads to HSF1 activation. We then aim to determine the effects of HSF1 activation in the growth and malignancy of breast cancer cells. We will first examine whether the transcriptional activation of hsp gene by HSF1 leads to inhibition of programmed cell death (PCD) in breast cancer cells exposed to heregulin. Such a decrease would increase tumor growth by upsetting the balance between cell growth and death and would also inhibit the effects of cytotoxic therapies in breast cancer treatment. Another consequence of HSF1 elevation is the enhanced transcriptional repression of genes that deter invasion and metastasis. We aim to examine the role of HSF1 in binding to the gene co- repressor metastasis associated protein 1 (MTA1) in gene repression in breast cancer. We will finally assess the rate at which changes in expression of HSF1, Hsps and MTA1 occur in breast carcinoma tissues from human patients. Our ultimate goals are (1) to use the data derived from mechanistic studies of HSF1 and its interacting proteins to design novel approaches to treating breast carcinoma and (2) to assess HSF1 and HSF1/MTA1 ratios as prognostic indicators of breast cancer response to therapy.